Heat the olive oil in a large, heavy-based saucepan over a moderate heat. Add the potatoes and cook for a few minutes, stirring frequently. Add the infused stock and paprika and stir well. Bring to the boil, then add the mussels, cockles (if available), sea bass and prawns.
Reduce the heat and simmer very gently for 10 minutes. Discard any mussels and cockles that haven't opened. Remove from the heat and adjust the seasoning to taste using the cayenne pepper, lemon juice and seasoning.
Serve from the dish.